We may next institute a comparison of Kant with the metaphysics of the empirical school. Natural plain Empiricism, though it unquestionably insists most upon sensuous perception, still allows a super-sensible world or spiritual reality, whatever may be its structure and constitution, and whether derived from intellect, or from imagination, &c. So far as form goes, the facts of this super-sensible world rest on the authority of mind, in the same way as the other facts, embraced in empirical knowledge, rest on the authority of external perception. But when Empiricism becomes reflective and logically consistent, it turns its arms against this dualism in the ultimate and highest species of fact; it denies the independence of the thinking principle and of a spiritual world which developes itself in thought. Materialism or Naturalism, therefore, is the consistent and thorough-going system of Empiricism. In direct opposition to such an Empiricism, Kant asserts the principle of thought and freedom, and attaches himself to the first-mentioned form of empirical doctrine, the general principles of which he never departed from. There is a dualism in his philosophy also. On one side stands the world of sensation, and of the understanding which reflects upon it. This world, it is true, he alleges to be a world of appearances. But that is only a title or formal description; for the source, the facts, and the modes of observation continue quite the same as in Empiricism. On the other side and independent stands a self-apprehending thought, the principle of freedom, which Kant has in common with ordinary and bygone metaphysic, but emptied of all that it held, and without his being able to infuse into it anything new. For, in the Critical doctrine, thought, or, as it is there called, Reason, is divested of every specific form, and thus bereft of all authority. The main effect of the Kantian philosophy has been to revive the consciousness of Reason, or the absolute inwardness of thought. Its abstractness indeed prevented that inwardness from developing into anything, or from originating any special forms, whether cognitive principles or moral laws; but nevertheless it absolutely refused to accept or indulge anything possessing the character of an externality. Henceforth the principle of the independence of Reason, or of its absolute self-subsistence, is made a general principle of philosophy, as well as a foregone conclusion of the time.